{"id":23702,"date":"2025-06-12T11:22:30","date_gmt":"2025-06-12T03:22:30","guid":{"rendered":"https:\/\/www.meetyoucarbide.com\/?p=23702"},"modified":"2025-06-12T11:22:30","modified_gmt":"2025-06-12T03:22:30","slug":"ultrafine-grained-cemented-carbide","status":"publish","type":"post","link":"https:\/\/www.meetyoucarbide.com\/it\/ultrafine-grained-cemented-carbide\/","title":{"rendered":"Research Status of Ultrafine-Grained Cemented Carbides, Part 1: Technological Development in Ultrafine Powder Production"},"content":{"rendered":"
Ultrafine-grained cemented carbides refer to materials with WC grain sizes ranging from 0.5 \u03bcm to 0.1 \u03bcm or even below 0.1 \u03bcm. The refinement of WC grains significantly enhances the mechanical properties of cemented carbides, making ultrafine-grained cemented carbides with finer WC grains a hot research topic globally. The key to preparing ultrafine-grained cemented carbides lies in three critical factors: powder raw materials, grain growth inhibitors, and sintering process technologies. These factors are interrelated and must be comprehensively considered to achieve high-performance, structurally stable, and homogeneous ultrafine-grained cemented carbides.<\/p>\n

This article focuses on introducing suitable powder raw materials for ultrafine-grained cemented carbides. Our next two weeklies will delve into the topics of grain growth inhibitors and sintering processes.<\/p>\n

 <\/p>\n

Quality Requirements for Powder Grains<\/h1>\n

The primary prerequisite for preparing ultrafine-grained or nanocrystalline cemented carbides is the production of ultrafine\/nano WC powder or WC-Co composite powder, which has become a current research focus. According to relevant literature, ultrafine\/nano powder raw materials must meet stringent criteria, including uniform average grain size with a narrow distribution, high purity, and reasonable carbon and oxygen content. Additionally, factors such as particle morphology, crystallographic perfection, and subgrain size directly influence the performance of ultrafine-grained cemented carbides.<\/p>\n

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Achievements in Powder Production<\/h1>\n

In 1989, Rutgers University in the United States took the lead in successfully developing nanostructured cemented carbides. Subsequently, Nanodyne Company developed nanostructured WC-Co cemented carbide composite powder with a particle size of 40 nm based on this foundation. Renowned companies in Japan, Switzerland, Germany, and other countries have also successively developed nanostructured cemented carbides. Among them, Switzerland’s Sandvik Company’s T002 ultrafine-grained cemented carbide has the finest grains, reaching 200 nm. Domestically, Zigong 746 Factory and Zhuzhou 601 Factory have both developed their own nanostructured cemented carbides, with grain sizes less than 500 nm, hardness of 93 HRA, and strength of 4000 MPa.<\/p>\n

 <\/p>\n

Technological Development in Ultrafine-Grained Cemented Carbide Powder Production<\/h1>\n

In summary, the preparation technologies for ultrafine\/nano-grained cemented carbide powders at home and abroad mainly include the following aspects:<\/p>\n

(1) Oxide Reduction-Carbonization Technology<\/h2>\n

This method involves granulating a mixture of WO and carbon black, followed by low-temperature carbonization reduction under N\u2082and H\u2082atmospheres to produce ultrafine WC with a grain size of 0.5 \u03bcm. This technology was jointly developed by Tokyo Tungsten and Sumitomo Electric in Japan. Its characteristics include rapid and continuous production of ultrafine and uniform WC powder, with the finest WC powder achieving a BET grain size of 0.11-0.13 nm. However, its drawback is that during the carbonization reduction process, H\u2082 reacts chemically with carbon black, making it difficult to control the carbon content in the product. The U.S. company EMO introduced the Rapid Carbonthermal Reduction (RCR) technology from Dow Chemical, operating at temperatures of 1500-2000\u00b0C. This technology is characterized by low cost and mass production capabilities, yielding WC powders with grain sizes of 0.2 \u03bcm, 0.4 \u03bcm, and 0.8 \u03bcm.<\/p>\n

\"\"<\/p>\n

Domestically, significant progress has also been made in this technology. Wuhan University of Technology has improved the oxide reduction-carbonization process by employing vacuum or inert gas atmospheres, thereby avoiding the adverse effects of H\u2082 on the reduction products and successfully producing ultrafine WC-Co composite powders with grain sizes ranging from 0.1 to 0.3 \u03bcm.<\/p>\n

Advantages:<\/p>\n

Enables rapid and continuous production, with the finest grain size reaching 0.11-0.13 \u03bcm (BET method).<\/p>\n

Low cost and suitable for large-scale production (e.g., EMO’s mass production of 0.2-0.8 \u03bcm WC powders).<\/p>\n

Svantaggi:<\/p>\n

H\u2082 reaction with carbon black makes carbon content control challenging.<\/p>\n

Although vacuum\/inert gas atmospheres mitigate this issue, they increase process complexity.<\/p>\n

 <\/p>\n

(2) Low-Temperature Reduction-Carbonization Technology<\/h2>\n

This method involves reducing blue or purple tungsten oxide with hydrogen gas at low temperatures to produce tungsten powder, which is subsequently carbonized into ultrafine WC powder. This technique is widely adopted in China, with notable users including Xiamen Golden Egret Special Alloy Co., Ltd., Zhuzhou Cemented Carbide Group, and Zigong Cemented Carbide Plant.<\/p>\n

Advantages:<\/p>\n

Simple process and extensive domestic application (e.g., Xiamen Golden Egret, Zhuzhou Cemented Carbide Group).<\/p>\n

Low equipment requirements.<\/p>\n

Svantaggi:<\/p>\n

Insufficient precision in carbon content control, necessitating inhibitor optimization.<\/p>\n

Potential limitations in grain size distribution uniformity.<\/p>\n

 <\/p>\n

(3) Thermochemical Synthesis Technology (Spray Drying)<\/h2>\n

Thermochemical synthesis, or spray drying, comprises three main steps: (a) preparing cobalt solutions from ammonium metatungstate and cobalt chloride or ethylenediamine tungstate, followed by homogeneous mixing; (b) spray-drying the mixture to obtain ultrafine and uniform cobalt-cobalt salt composite powders; and (c) reducing and carbonizing the powders in a fluidized bed reactor to produce nano WC-Co composite powders. Characteristics: The nano WC-Co composite powders retain the morphology of the precursors, with grain sizes controllable by adjusting reaction temperature, holding time, and carbonization gas activation. They exhibit high specific surface area and enable alloy densification at relatively low temperatures. Disadvantages: The process is complex, and carbon content control is inaccurate, though controllability can be improved by effectively blending carbonization atmospheres as carbon sources.<\/p>\n

Advantages:<\/p>\n

Controllable grain size (via temperature, time, and carbonization atmosphere adjustments).<\/p>\n

High specific surface area and excellent low-temperature densification performance.<\/p>\n

Svantaggi:<\/p>\n

Complex process and challenging carbon content control.<\/p>\n

Requires carbonization atmosphere regulation for stability.<\/p>\n

\"\"<\/p>\n

(4) In-Situ Carburization Technology<\/h2>\n

In-situ carburization involves directly reducing precursors to single-phase nano WC-Co<\/a> composite powders using hydrogen gas without external carbon sources (e.g., CO\/CO\u2082). This is achieved by dissolving tungstic acid and cobalt salt in a polyacrylonitrile solution, followed by low-temperature drying and reduction in a 90% Ar-10% H\u2082 mixed gas atmosphere at 800-900\u00b0C, yielding WC-Co powders with grain sizes of 50-80 nm. This method was first reported by Y.T. Zhou of the University of Texas in 1994. Key Innovation: Replacing CO\/CO\u2082 mixtures with polyacrylonitrile as the in-situ carbon source, enabling direct hydrogen reduction of precursors to single-phase nano WC-Co composites. Process parameters such as reduction temperature, atmosphere, and trace cobalt acetate catalyst additives significantly influence the final nano composite powder quality. Disadvantages: Insufficient reduction due to shortened diffusion times results in residual undecomposed polymers or free carbon, adversely affecting product performance.<\/p>\n

Advantages:<\/p>\n

Highly innovative, achieving grain sizes of 50-80 nm.<\/p>\n

Simplifies the process by eliminating traditional carbon sources (e.g., CO\/CO\u2082).<\/p>\n

Svantaggi:<\/p>\n

Incomplete reduction leads to residual polymer or free carbon, impacting performance.<\/p>\n

High sensitivity to temperature, atmosphere, and catalysts (e.g., cobalt acetate).<\/p>\n

\"\"<\/p>\n

(5) Plasma Technology<\/h2>\n

Plasma technology utilizes a plasma-generated heat source maintained at 4000-5000\u00b0C to decompose, react, and synthesize raw materials (W, WC, or WO\u2083) and carbon sources (CH\u2084), yielding products with grain sizes as fine as 5-20 nm. The primary heat sources include direct current (DC) plasma, high-frequency plasma, or a combination of both. Disadvantages: Plasma sustainability is poor, making it difficult to ensure complete evaporation and reaction of the raw materials.<\/p>\n

Advantages:<\/p>\n

Produces extremely fine grain sizes (5-20 nm), suitable for ultra-high-end applications.<\/p>\n

Rapid reaction rates.<\/p>\n

Svantaggi:<\/p>\n

Poor plasma stability leads to incomplete raw material evaporation and reactions.<\/p>\n

High equipment costs and energy consumption.<\/p>\n

 <\/p>\n

(6) Sol-Gel Technology<\/h2>\n

The sol-gel process involves the hydrolysis and polycondensation of hydrolyzable metal compounds in a solvent, followed by gelation, drying, and reduction to produce nanostructured powders. This low-temperature process relies on hydrolysis and polymerization reactions, resulting in high-purity powders with narrow grain size distributions, high chemical activity, and homogeneous multi-component mixtures. For instance, scientists like Srikanth Rahunathan have utilized sol-gel technology to develop nano W-Co, W-Mo, and W-Cu composite powders. Characteristics: The sol-gel method offers precise chemical controllability, simple operation, and low cost for producing nanostructured composite powders with uniform structures. Disadvantages: The process is complex and challenging to scale for mass production.<\/p>\n

Advantages:<\/p>\n

High purity, narrow grain size distribution, and controllable chemical activity.<\/p>\n

Suitable for multi-component composite powders (e.g., W-Co, W-Mo).<\/p>\n

Svantaggi:<\/p>\n

Complex preparation process and difficulty in large-scale production.<\/p>\n

Higher costs and longer production cycles.<\/p>\n

 <\/p>\n

(7) Mechanical Cemente Carbide<\/a> Alloying Technology<\/h2>\n

Mechanical alloying involves blending elemental powders in specific ratios and milling them under inert gas protection in a high-energy ball mill. Mechanical energy from milling induces repeated deformation, cold welding, and fracturing of the powders, resulting in a dispersion of ultrafine particles and solid-state alloying. Advantages: The process is technically simple, requires minimal equipment, and is easy to operate. Disadvantages: Alloying may introduce impurities, and internal stresses\/agglomeration within the powders due to compressive\/shear forces can negatively impact compressibility and sintering behavior.<\/p>\n

Advantages:<\/p>\n

Simple technology, inexpensive equipment, and ease of operation.<\/p>\n

Svantaggi:<\/p>\n

Risk of impurity introduction during alloying.<\/p>\n

Significant internal stresses and severe agglomeration in powders, affecting compaction and sintering properties.<\/p>\n

\"cemented<\/p>\n

Domestically, the Institute of Physics, Chinese Academy of Sciences, successfully produced nano WC powder with a grain size of 7.2 nm using mechanical alloying in 1944. Similarly, Professor Wu Xijun of Zhejiang University synthesized nano single-phase W\u2082C powder with an average grain size of 6.0 nm using the same method.<\/p>\n

Advantages:<\/p>\n

Simple equipment and easy operation.<\/p>\n

Capable of producing extremely fine grain sizes (e.g., 7.2 nm WC powder).<\/p>\n

Svantaggi:<\/p>\n

High risk of impurity introduction.<\/p>\n

Significant internal stress in powders and severe agglomeration, adversely affecting compaction and sintering properties.<\/p>\n

 <\/p>\n

Riepilogo<\/h1>\n

For the production of ultrafine-grained cemented carbide powders:<\/p>\n

1.Oxide reduction-carbonization and low-temperature reduction-carbonization technologies are suitable for large-scale production due to their low cost and mature processes. Plasma and sol-gel technologies can produce nano-scale powders but require addressing stability and cost challenges.<\/p>\n

2.In-situ carburization introduces polymer-based carbon sources as an innovative approach to carbon content control, though optimization of reduction completeness is needed.<\/p>\n

3.Institutions such as Wuhan University of Technology and the Institute of Physics, Chinese Academy of Sciences, have achieved notable advancements in improving conventional processes (e.g., vacuum carbonization, mechanical alloying). However, high-end powders (e.g., sub-50 nm grades) still rely on imports.<\/p>\n

 <\/p><\/div>\n

<\/p>","protected":false},"excerpt":{"rendered":"

Ultrafine-grained cemented carbides refer to materials with WC grain sizes ranging from 0.5 \u03bcm to 0.1 \u03bcm or even below 0.1 \u03bcm. The refinement of WC grains significantly enhances the mechanical properties of cemented carbides, making ultrafine-grained cemented carbides with finer WC grains a hot research topic globally. The key to preparing ultrafine-grained cemented carbides…<\/p>","protected":false},"author":2,"featured_media":23706,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[79],"tags":[],"class_list":["post-23702","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-materials-weekly"],"jetpack_featured_media_url":"https:\/\/www.meetyoucarbide.com\/wp-content\/uploads\/2025\/06\/\u56fe\u72474-1.png","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.meetyoucarbide.com\/it\/wp-json\/wp\/v2\/posts\/23702","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.meetyoucarbide.com\/it\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.meetyoucarbide.com\/it\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.meetyoucarbide.com\/it\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.meetyoucarbide.com\/it\/wp-json\/wp\/v2\/comments?post=23702"}],"version-history":[{"count":1,"href":"https:\/\/www.meetyoucarbide.com\/it\/wp-json\/wp\/v2\/posts\/23702\/revisions"}],"predecessor-version":[{"id":23707,"href":"https:\/\/www.meetyoucarbide.com\/it\/wp-json\/wp\/v2\/posts\/23702\/revisions\/23707"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.meetyoucarbide.com\/it\/wp-json\/wp\/v2\/media\/23706"}],"wp:attachment":[{"href":"https:\/\/www.meetyoucarbide.com\/it\/wp-json\/wp\/v2\/media?parent=23702"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.meetyoucarbide.com\/it\/wp-json\/wp\/v2\/categories?post=23702"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.meetyoucarbide.com\/it\/wp-json\/wp\/v2\/tags?post=23702"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}